The present invention relates to hydrocarbon soluble or dispersible hydrogenated phospholipids and their utility as an additive for oleaginous compositions including, fuel oils, lubricating oils, greases, industrial oils, gear oils, power transmitting fluids, and engine lubricating oils.
There are many instances, as is well known, particularly under boundary lubrication conditions where two moving surfaces in contact with each other must be lubricated, or otherwise protected, so as to prevent wear, and to insure continued movement. There are other instances where friction between two rubbing surfaces is sought to be modified but not necessarily minimized. By controlling friction between two surfaces, the power required to impart movement from one surface to another is also controlled.
For example, a specialized property sought to be imparted to certain lube oil compositions adapted for use as an automatic transmission fluid is the friction modification characteristic of the fluid. This property distinguishes automatic transmission fluids (ATF) from other lubricants, and in fact between types of ATF as well. Accordingly, such friction modification characteristic has received the most attention by both the transmission manufacturers and fluid producers for many years. This attention stems from the fact that the friction requirements of an ATF are unique and depend on the transmission and clutch design, as well as on the type of clutch plate material used.
Another property sought to be imparted to lubricating oil compositions, including automatic transmission fluids, is reduced wear such as bearing and power component wear.
As is also well known, both wear and friction modification can be controlled through the addition of suitable additives with varying degrees of success.
While there are many known additives which may be classified as anti-wear, or friction modifying agents, it is also known that many of these additives act in a different physical or chemical manner and often compete with one another, e.g. they may compete for the surface of the moving metal parts which are subjected to lubrication. Accordingly, extreme care must be exercised in the selection of these additives to insure compatibility and effectiveness.
The metal dihydrocarbyl dithiophosphates are one class of additives which are known to exhibit antioxidant and anti-wear properties. The most commonly used additives of this class are the zinc dialkyl dithiophosphates (ZDDP) which are conventionally used in lubricant compositions. While such zinc compounds afford excellent oxidation resistance and exhibit superior anti-wear properties, they can be corrosive.
Both anti-wear and friction modifying agents function by forming a coating on the surface of the moving metal parts. The coating bonds are generally effected physically and/or chemically. Consequently, if the bonding between the anti-wear agent and the metal part is stronger than the bonding between the friction modifying agent and the metal part, the anti-wear agent will displace the friction modifying agent at metal surface, i.e. at the metal/fluid lubrication boundary interface. This results in a loss in the ability of the friction modifying agent to exert its intended effect.
Various tests have been designed by auto manufacturers for measuring ATF friction and anti-wear properties which if passed, are indicative of the fact that such properties will match the requirements of particular transmission designs and result in transmission durability and smooth shifting under a variety of road conditions.
Friction modification is typically evaluated on an SAE No. 2 friction apparatus. In this test, the motor and flywheel of the friction machine (filled with fluid to be tested) are accelerated to constant speed, the motor is shut off and the flywheel speed is decreased to zero by application of the clutch. The clutch plates are then released, the flywheel is again accelerated to constant speed, and the clutch pack which is immersed in the test fluid is engaged again. This process is repeated many times with each clutch engagement being called a cycle.
During the clutch application, friction torque is recorded as a function of time. The friction data obtained are either the torque traces themselves or friction coefficients calculated from the torque traces. The shape of the torque trace desired is set by the auto manufacturers. One way of expressing this shape mathematically, is to determine the torque: (a) when the flywheel speed is midway between the maximum constant speed selected and zero speed (such torque measurement is referred to herein as T.sub.D) and (b) when as the flywheel speed approaches zero rpm (such torque measurement is referred to herein as T.sub.O). Such torques can then be used to determine the torque ratio which is expressed as T.sub.O /T.sub.D, in which case the typical optimum value thereof is 1, or alternatively, to determine the torque differential T.sub.O -T.sub.D ; the typical optimum value of which is 0. (Thus, the optimum target value is achieved when T.sub.O =T.sub.D provided T.sub.D is within acceptable limits.) As the T.sub.O /T.sub.D increasingly exceeds 1, a transmission will typically exhibit shorter harsher shifts as it changes gears. On the other hand as T.sub.O /T.sub.D decreases below 1, there is an increasingly greater danger of clutch slippage when the transmission changes gears. Similar considerations apply with respect to T.sub.O -T.sub.D relative to the O target value.
While many automatic transmission fluids can achieve target values of T.sub.O /T.sub.D after a minimum number of cycles, it becomes increasingly more difficult to sustain such target values as the number of cycles is increased. The ability of an ATF to sustain such desired friction properties is referred to herein as friction stability. It is believed that as the ATF ages under the influence of the heat of friction, the anti-wear agent can break down and the decomposition products displace conventional friction modifiers at the metal/fluid lubrication boundary interface. As a result, the fluid may exhibit varying properties.
Attempts to solve the problem of friction instability by simply adding more friction modifier have not met with success because this tends to reduce the breakaway static torque (T.sub.S) of the fluid. This parameter when expressed as the breakaway static torque ratio (T.sub.S /T.sub.D) reflects the relative tendency of engaged parts, such as clutch packs, bands and drums, to slip under load. If this value is too low, the slippage can impair the driveability and safety of the vehicle.
Thus, transmission designs have undergone radical changes, thereby necessitating the formulation of ATF additives capable of meeting new and more stringent property requirements needed to match such design changes.
No base oil alone can even approach the many special properties required for ATF service. Consequently, it generally is necessary to employ several chemical additives, each of which is designed to impart or improve a specific property of the fluid.
Accordingly, there has been a continuing search for new additives possessed of one or more properties which render them suitable for use in ATF compositions, as well as other oleaginous compositions. The present invention was developed in response to this search.
The prior art contains many examples of improved oleaginous lubricating compositions wherein a phospholipid material such as lecithin is added to an oleaginous material.
For example, U.S. Pat. Nos. 2,216,711 and 2,302,708 disclose processes for improving lubricating oils by adding to the oils an amount of phosphatide material such as lecithin. The phosphatide material is not substantially saturated, e.g., hydrogenated.
U.S. Pat. Nos. 2,221,162 and 2,244,416 also relate to lubricant compositions comprising a phosphatide material, a lubricating oil, and other additives. Again, the phosphatide material is not hydrogenated.
Other patents which disclose the use of a phospholipid such as lecithin in a lubricating oil composition include U.S. Pat. Nos. 2,257,601, 2,270,241, and 2,285,854. In each of these patents, the phospholipid material is not hydrogenated.